1. Field of the Invention
The present invention relates to a charged particle beam writing apparatus and a charged particle beam writing method. For example, the present invention relates to a method for correcting dimension variation of a pattern due to electron back scattering in electron beam writing.
2. Description of Related Art
The lithography technique that advances microminiaturization of semiconductor devices is extremely important as being a unique process whereby patterns are formed in the semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. In order to form a desired circuit pattern on semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a highly precise master pattern.
FIG. 10 is a schematic diagram explaining operations of a conventional variable shaped electron beam (EB) writing (or drawing) apparatus. As shown in the figure, the variable shaped electron beam writing apparatus operates as described below. A first aperture plate 410 has a quadrangular opening 411 for shaping an electron beam 330. A second aperture plate 420 has a variable-shape opening 421 for shaping the electron beam 330 having passed through the opening 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector to pass through a part of the variable-shape opening 421 of the second aperture plate 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g. x direction) during the writing. In other words, a quadrangular shape that can pass through both the opening 411 and the variable-shape opening 421 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the X direction. This method of forming a given shape by letting beams pass through both the opening 411 of the first aperture plate 410 and the variable-shape opening 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) method.
In the electron beam writing, a phenomenon called a proximity effect occurs when electron beams irradiate a circuit pattern on a mask with resist to write or “draw” a pattern. The proximity effect is generated by backward scattering of electron beams penetrating the resist film, reaching the layer thereunder to be reflected, and entering the resist film again. As a result, a dimensional variation occurs, that is, a written pattern is deviated from a desired dimension. Therefore, in the electron beam writing, proximity effect correction that suppresses such dimensional variation by correcting a dose is performed, for example.
In such electron beam writing, there is a case in which a pattern, such as a scattering bar, narrower than other pattern is written with a larger dose than that of other pattern. Moreover, there is a case in which writing conditions (parameters, such as a dose and a proximity effect correction coefficient) of only a certain region is changed in order to resize a pattern in the region by using a dose. Furthermore, there is a case in which writing is to be performed again after changing the writing conditions for a region which has been written once. In the cases described above, it is necessary to perform proximity effect correction respectively for the patterns of different writing conditions.
However, in performing proximity effect correction for a target pattern, if a pattern using writing conditions different from those of the target pattern is arranged near the target pattern, the influence of the pattern of different writing conditions needs to be taken into consideration. Generally, since parameters for proximity effect correction are different from each other between patterns of different writing conditions, it is difficult to apply an existing model proximity effect correction equation to a closely arranged pattern of different writing conditions. Moreover, even if the proximity effect correction is performed using a parameter according to conditions of one pattern in the patterns of different writing conditions, it is difficult to perform proximity effect correction in sufficient accuracy.
Now, there is a proximity effect correction coefficient η which is suitable for performing proximity effect correction for each base dose Dbase. Then, a method of calculating a dose for correcting a dimension variation amount due to a loading effect while correcting a proximity effect with changing a combination of the base dose Dbase and the proximity effect correction coefficient η is disclosed (refer to, e.g., Japanese Patent Application Laid-open (JP-A) No. 2007-150243).